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Application Note: Key Features of Ricoh's Real Time Clocks

1. Programmable Calibration Adjustment

Programmable Calibration Adjustment*) Ricoh RTCs perform this calibration adjustment every 20 or 60 seconds.
(Notes: R2025/R2045 performs a calibration adjustment evey 20 seconds.)

Ricoh RTCs have a programmable calibration adjustment from −189 ppm to +189 ppm or −63 ppm to +63 ppm.
The crystal oscillator used in Ricoh RTCs provides 32,644 to 32,892 pulses per 20 seconds or 60 seconds while a normal crystal oscillator provides exactly 32,768 pulses per second.

Tuning fork crystal provides highly stable natural oscillation frequency; however, environmental changes of temperature, humidity, pressure, vibration or a capacitance formed on a substrate can change the resonant frequency of a crystal oscillator.

When performing a capacitor matching evaluation using a PCB for mass production, those influences need to be considered. Ricoh RTCs have a programmable time register to adjust a timekeeping glitch without the need of additional capacitors, which makes the capacitor matching evaluation easier.

A tuning fork crystal is usually cut such that its frequency over temperature is a parabolic curve centered around 25°C. Ricoh's programmable calibration circuit have an external temperature sensor to compensate this deviation.

Uncompensated Crystal Drift

Uncompensated Crystal Drift

Ricoh RTCs Compensated Crystal Drift

Ricoh RTCs Compensated Crystal Drift

2. Clock Data Validation

These RTCs provide a power-on reset function, an oscillation halt sensing function and a supply voltage monitoring function.
These functions can be applied to judge a clock data validity.

  • Power-on Reset Function
    Power-on reset circuit is configured to reset a control register and store the status as a flag after initial power on from 0 V without backup battery.
  • Oscillation Halt Sensing Function
    Oscillation halt sensing circuit is equipped with internal registers configured to record any past oscillation halt as a flag.
  • Supply Voltage Monitoring Function
    Supply voltage monitoring circuit is configured to record a drop in supply voltage below supply voltage monitoring thresholds.

Power-on Reset/ Oscillation Halt Sensing/ Supply Voltage Monitoring Included

4-Wire (SPI Bus)

2-Wire (I2C Bus)

3. Battery Backup Switch-over Circuit

These RTCs have a backup battery switch-over circuit which detects power failures and automatically switches to the battery supply when a power failure occurs. They are also equipped with two or three power supply pins so there is no need of adding a diode.

Battery Backup Switch-over Circuit

Notes: R2062 does not have the SW2 switch or the VSB pin. R2262 has the SW2 switch and the BAT pin instead of the VSB pin.
The SW2 switch is constantly turned on unless it is turned off by a register setting.

Battery Backup Switch-over Circuit Included

3-Wire

2-Wire (I2C Bus)

4. High-precision Real Time Clock Module

These RTCs have a built-in crystal oscillator that is adjusted to 0±5 ppm at 25°C at the time of factory shipping. This means ±13 seconds per month at 25°C.

Crystal Oscillator Included

4-Wire (SPI Bus)

2-Wire (I2C Bus)

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